1. Field of the Invention
The present invention relates to a process for stabilizing an adjuvant containing vaccine composition, an adjuvanted vaccine composition in dry form and in particular a process for stabilizing an influenza vaccine composition, particularly an adjuvanted influenza vaccine composition in dry form.
2. Description of Related Art
U.S. Pat. No. 3,655,838 discloses a method of pelletizing analytical or immunological reagents by freezing droplets of solutions in a freezing medium, such as liquid nitrogen, and subsequent freeze drying in order to obtain freeze-dried, reagent containing micro-particles, spherical beads or lyospheres. EP 0 081 913 B1 describes a method for producing spherical frozen particles by freezing droplets in an inert liquid freezing medium with a higher density than the droplets and removing the frozen particles from the surface of the liquid freezing medium. WO 94/25005 discloses the stabilization of gonadotropin in lyospheres, a method for making such lyospheres and pharmaceutical preparations comprising the same. EP 0 799 613 (U.S. Pat. No. 5,897,852) discloses a vaccine pack that comprises a vaccine container containing one ore more freeze-dried bodies containing the vaccine components, at least one of which being a lyosphere or micro-particle having a diameter of at least 0.2 mm. WO 2006/008006 (US 2008/0060213) discloses a process for producing containers filled with a freeze-dried product wherein droplets of the product are frozen to form pellets, the pellets are freeze dried, assayed and loaded into the containers. Other techniques for obtaining frozen particles or pellets are known for application in the food industry (e.g. U.S. Pat. No. 5,036,673 or US 2007/0281067 A1).
The freeze drying technology allows improving the stability of a lot of products which can be a vaccine with or without adjuvant. For example EP 0 475 409 discloses a method for preserving a buffer and optionally a cryoprotectant containing suspension of microscopic biological material by nebulizing the suspension to microdroplets, freezing the droplets on a rotating cryogenic surface and drying the microdroplets. Preferably the droplets have a diameter of about less than 200 μm.
The freeze-drying of flu antigens has been studied in the literature and a detailed review is available (Amorij et al. 2008: Development of stable Influenza vaccine powder formulations: challenges and possibilities. Pharmaceutical Research, Vol 25, 1256-1273). U.S. Pat. No. 3,674,864 discloses a process for stabilizing influenza virus vaccines essentially by suspending the virus in an aqueous sucrose containing solution and freeze-drying the suspension. Also the stabilization of tetanus and diphtheria toxoids has been discussed in the literature (see e.g. S. P. Schwendeman et al., Proc. Natl. Acad. Sci. USA Vol. 92, pp. 11234-11238, 1995). Very recently, optimized formulations for lyophilizing tetanus toxoid have been proposed (P. Matejtschuk et al. Biologicals 37 (2009) 1-7).
Usually the freeze drying is a final step in the pharmaceutical industry, coming after the filling step in vials, syringes or larger containers. In this case the dried product has to be rehydrated (synonyms in this document: reconstituted or dissolved) before its use.
Freeze drying in the form of micropellets allows the same stabilization of the dried vaccine product as for mere freeze-drying alone or it improves stability for storage. Furthermore, the micropellets technology offers several advantages in comparison to the current freeze drying, since it allows e.g.                blending of the dried products before filling (or by sequential filling)        titer adjustment before filling (which can be used in case of stock piling)        minimizing the interaction between products (there is only product interaction after rehydration), and        improvement of the stability in some cases.        
For these reasons the advantage of the micropellets technology allows several approaches for the drying of adjuvanted vaccine:                The drying of the antigens together with the adjuvant (being in the same phase): to stabilize the two (antigens and adjuvant) and to stabilize the interaction between them by trapping them in a glassy matrix in which all molecular motions and chemical reactions are greatly hindered. This solid state allows to maintain throughout storage (even at higher temperature) potency of the antigen, physical and immunological properties of the adjuvant and nature and force of the interaction between the two.        The drying of the antigens and the separate drying of the adjuvant (antigen and adjuvant being in different phases), followed by blending of the two before the filling or by a sequential filling. In some cases, stability of the adjuvant alone can be a problem (chemical stability of emulsions, physical stability of aluminum gels, liposomes and others . . . ) at the liquid state for long-term storage at +5° C. or higher or at lower temperatures. The micropellet technology allows improving stability of the adjuvanted vaccine by generating separate micropellets of antigen and adjuvant. The stabilizing formulation can be optimized independently for each antigens and the adjuvant. The micropellets of antigens and adjuvants can be then subsequently filled into the vials or blended before filling into the vials. The separated solid state allows to avoid throughout storage (even at higher temperature) interactions between antigen and adjuvant, to maintain the potency of the antigen and physical and the immunological properties of the adjuvant. In such a configuration, the content of the vial can be more stable than any other configurations with either one of the antigens or the adjuvants in the liquid state or when antigens and adjuvant are dried within the same pellets. Interactions between antigens and adjuvants are this way standardized as they occur only after rehydration of the dry combination with a selected diluent which may comprise water for injection, buffers and stabilizing excipients. Interactions are therefore to be controlled only during the short period of time between rehydration and injection of the vaccine.        
It is therefore possible to improve the overall stability of the two products can be improved (optimization of the formulation for each product and not a compromise for the two together) and the vaccine itself, adjust the titer of one out of the two after the storage and before filling, to facilitate the manufacturing process by separation of the two products drying.